Production of rayon



.946- w. F. UND'ERWOOD 2,413,123

PRODUCTION OF RAYON Filed June '29, 1944 A TTORNEY 2 INVENTOR.

Patented Dec. 24, 1946 PRODUCTION OF RAYON William Frederick Underwood, Oak Ridge, Tenn.,

assignor to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware Application June 29, 1944, Serial No. 542,698

This invention relates to the production of rayon, and more particularly, it relates to the production of regenerated cellulose fibers, filaments, yarns, and the like, having an inherent and permanent crimp.

U. 8. Patent No. 2,249,745 discloses a new procass for the production of new and unique regenerated cellulose fibers, filaments and yarns having an inherent and permanent crimp. The process of the above-said patent comprises extruding viscose, in the form of filaments, into a setting bath which has a sufiiciently rapid -c agulating action, relative to any regenerating action thereof, to completely coagulate said filaments prior to any substantial regeneration thereof, drawing said filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of draw-oil.

The .coagulated filaments may then be regenerated, for example, by subjecting the same to the the action of an acid regenerating bath. The filaments are then purified and dried, the drying preferably taking place with the filaments in a free, loose condition.

The resulting filaments are substantially noncrenulated, have a strength of between 0.5 and 1.25 grams per denier, and have permanent crimps lying at random in three dimensions. By the term permanent crimp is meant that the filaments or yarns may be wet with water, then stretched over that required to straighten the filaments, and allowed to dry in this stretched condition without destroying the inherent nature of the filaments to again regain their crimp by again wetting the same and permitting them to dry in the absence of tension.

Although yarns and filaments produced in accordance with the process of the above-said patent have found many practical commercial uses, they possess some physical characteristics which can be considerably improved. They have a lowtenacity (between 0.5 and 1.25 grams per denier), a high elongation (of the order of 60% dry elongation and 35% wet elongation), a high spontaneous elongation in water (50% or more), and a high degree of secondary swelling (of the order of 150%). The latter two characteristics prevented the satisfactory use of the yarn in fiat woven fabrics such as suitings, overcoat fabrics and the like. Furthermore, the above-described filaments and yarns possess an,inherently dull, subdued, non-lustrous appearance which prevented its use in many types of fabri Also. they could not be easily produced in fine deniers,

6 Claims. (0!. 18-54) 2 thus limiting their use in heavy fabrics, or use as the pilein carpets and the like.

It is an object of this invention to provide a substantially non-crenulated, regenerated cellulose filament or yarn having an inherent and permanent three dimensional crimp and having a relatively high tenacity, a relatively low elongation, a low spontaneous elongation in water, and a low secondary swelling in water.

It is another object of this invention to provide a new and improved process for the production of crimped filaments which is not subject to the objections, above-stated.

It is another object of this invention to provide a new and improved spinning bath for the production of crimped filaments and yarns by spinning with a high iet-velocityzdraw-oif ratio.

Other objects of the invention will appear herelnafter.

The above objects may be accomplished by extruding viscose, in the form of filaments, into a setting bath comprising an aqueous solution containing sodium bisulfite, sodium sulfite, and sodium sulfate, which .bath has a pH value of between 5 and 6.5 and a sufiiciently rapid coagullating action, relative to any regenerating action thereof, to completely coagulate said filaments prior to any substantial regeneration thereof, drawing the filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of for , draw-oil, stretching the coagulated, substantially non-regenerated filaments at least over their straight length, (i. e., of their originally formed straight length) and regenerating,

and drying, the stretched filaments while maintaining them free from tension.

The invention will be more readilyunderstood by referring to the following detailed description when taken in connection with the accompanying illustrations, in which:

Fig. 1 is a diagrammatic, side elevational view, with parts shown in section, of an apparatus suitable for use in carrying out the process of the invention.

Fig. 2 is a similar diagrammatic, side elevational view of another form of suitable apparatus.

Referring to Fig. 1 of the drawing, reference numeral Ill designates a setting bath tank containing the sodium bisulfite-sodium sulfite-sodium sulfate setting bath. The viscose filamentforming composition is forced through candle filter l2, conduit I 4 and spinneret I6 under sufficient pressure that the velocity of extrusion of the filaments from the spinneret orifices is at least four times the velocity of draw-o8 by feedwheel 22. The filamentous solution buckles and bends as it is forced into the coagulating, substantially non-regenerating setting bath, thus forming highly crimped substantially nonoriented filaments l8. The filaments I! are brought together and passed about grooved guide rollers l9 and 20, and then about feed wheels 22 and 24. The yarn comprising the filaments II is passed about the feed wheels 22 and 24 with a suillcient number of turns to avoid slippage. The peripheral speed of feed wheel 24 is enough greater than that of feed wheel 22 to impart the desired amount of stretch to the yarn. From feed 24 the yarn is dropped onto endless belt 20. This endless belt 28 may comprise a perforated metal base member covered with a fabric which will support the yarn. Preferably the belt 28 is moved slowly to permit the yarn to pile up in tensionless ringlets thereon.

As the belt 25 moves along, it will carry the loose, untensioned yarn under regenerating bath shower 28, one or more purifying bath showers 32 and driers 30 and 38. The baths which are showered onto the yarn will pass through the belt, and will be caught in drip pans 30 and 24. The regenerated purified and dried yarn will then be wound onto a bobbin 40 or the like.

In Fig. 2 of the drawing; reference numeral 42 designates a pump by means of which the filament forming composition, for example, viscose, is forced through candle filter 44, conduit 46 and spinneret 48. The spinneret is positioned in a relatively deep setting bath tank 50 so as to provide a suitable head of bath liquid above the splnneret. A tube 52, having a length of from 12 to 36 inches, is positioned a short distance from the face of the spinneret 48. Bath liquid from tank 50 will flow through the tube 52 to carry the yarn 64 from the spinneret to squeeze rolls 54 and 58. The pump pressure of pump 42 and the head of bath liquid on the tube 52 are so adjusted that the velocity of extrusion of the filament-forming solution is at least four times the velocity of draw-ofl, the latter being approximately equal to the velocity of the liquid passing through tube 52.

The liquid passing from the open end of tube 52 is caught in receptacle 58, from which it may be returned to tank 50 by means of conduit 60 and pump 62. The yarn 64 is passed about squeeze rolls 54 and 56 in a path approximately a figure S to avoid slippage. The yarn is then passed about grooved guide rolls 88 and which are positioned in a tank 68 containing a stretching bath liquid. From guide roll 10, the yarn is p ssed through another set of squeeze rolls 12 and I4. Here again, the yarn is passed about and between the squeeze rolls in such a manner as to avoid slippage of the yarn. The squeeze rolls I2 and 14 are driven at a peripheral speed sufilciently greater than that of squeeze rolls 54 and 56 to stretch the yarn the desired amount.

From squeeze roll 14, the yarn 64 is passed around grooved guide rolls 18 and 80 which are positioned in tank 16 which contains a regenerating liquid, for example, an aqueous acid or a boiling bath having the same composition as the setting bath. The yarn is then passed onto a wind-up bobbin 82 or the like. If necessary to complete the regeneration, the bobbin 82 may be positioned in a bath of regenerating liquid for the required length of time. The yarn wound on the bobbin 82 may then be skeined and subjected to purification and drying procedures in a known manner. The drying of the yarn should be car- 4 ried out with the yarn free from tension to permi the free formation of crimps.

The following examples disclose, in specific detail, preferred methods for the practice of the invention, it being understood that the invention is not limited to the specific details set forth. In the examples parts referred to are parts by weight unless otherwise indicated.

Example I A viscose solution prepared from sulfite wood pulp and containing 7% cellulose and 4% sodium hydroxide, and possessing a viscosity at 20 0., of approximately 40 poises is ripened to a sodium chloride salt index of 4.0, after which it is extruded at the rate of 200 grams per minute through a spinneret possessing 500 holes, each hole being 0.00325 inch in diameter, into a bath containing 12% sodium bisulfite, 7% sodium sulfite and 10% sodium sulfate. The bath has a PE of 5.9 and is maintained at a temperature 55 C. The yarns are passed under the surface of the bath for a total distance of 45 inches after which they are withdrawn at a rate of 414 inches per minute, the ratio of Jet velocity to draw-oil speed is approximately 7.6. The yarns are then passed directly into a second bath of similar composition but heated to 100 C. wherein they are stretched to 185.5% of their original length, i, e., 85.5% over its original straight length. The stretched yarn is then collected in a tension-free condition in a container, the filled container being subsequently immersed in the stretching bath for a period of 60 minutes whereby the yarns are completely converted to regenerated cellulose. They are then washed free of acid and treated with a 0.5% aqueous solution of sulfonated tallow, after which they are dried in air at room temperature (approx. 20 C.) in a substantially tension-free condition. The dried yarns possess a dry tenacity of 1.25 grams per denier, a wet tenacity of 0.50 gram per denier, a dry elongation of 20% and a wet elongation of 4.5%. They are highly crimped. When placed in water, they undergo a spontaneous elongation of 35% and exhibit a secondary swelling of Example 11 The viscose solution of Example I was extruded at a rate of 95.9 grams per minute through a spinneret having 648 holes, each hole being 0.002 inch in diameter into a spinning bath containing 8.67% sodium bisulfite, 9.28% sodium sulfite and 10.22% sodium sulfate, together with 0.1% lauryl trimethyl ammonium bromide, the bath possessing a pH of 6.15 and being maintained at a temperature of 65 C. The yarn was led through the bath for a total travel of 50 inches after which it was withdrawn from the bath at a rate of 357 inches per minute. This corresponds to a ratio of jet velocity to draw-oil speed of 7.4. On leaving the spinning bath, the yarn was passed for a distance of 50 inches through a second bath of similar composition but heated to a temperature of C., the yarn being stretched 100%, i. e., to 200% of its original straight length, during its travel through this second bath. The stretched yarn was collected in a container under low tension and subsequently reeled to skeins which were immersed, loosely for 10 minutes in the stretching bath to effect complete regeneration of the yarn. The regenerated cellulose yarn was washed with soft water, treated with a sulfonated oil finish and dried in skeln form under substantially no tension. The dried yarn possessed ahigh degree of crimp, the crimp being three dimensional in nature and permanent. The filaments Possessed a smooth non-crenulated cross-section. The yarn possessed a denier per filament of 7.01 and had a dry tenacity of 1.46 grams per denier, a wet tenacity of 0.69 gram per denier, a dry elongation of 15.9%, a wet elongation of 4.2%. When immersed in water, it underwent a spontaneou elongation of 33.1% and showed a secondary swelling of 94.2%.

The process of the present invention may be carried out with the use of any viscose filamentforming composition heretofore used in the production of viscose rayon yarns. The viscose may contain, for example, between 5% and cellulose, 3% to 10% caustic soda, and. it may have a sodium chloride index of between 2 and 7. Preferably, however, viscose having a cellulose content of between 6% and 8%, a caustic soda content of between 4% and 7% and a sodium chloride index of between 3.5 and 6.0 is used. The

viscose may contain modifying agents, for example, delustering agents, dye adjuvants, heat stabilizing agents and the like. I

As already mentioned, the coagulating or setting bath employed in carrying out the present invention should contain sodium bisulfite, sodium sulfite and sodium sulfate in proportions to impart to the bath a pH value of between 5 and 6.5. The preferred baths contain between 6% and 20% of sodium bisulflte, between 3% and 10% of sodium sulfite and between 8% and 12% of sodium sulfate, depending upon the composition of the viscose used, the temperature of the setting bath, and the spinning speed. For example, when using a viscose having a low caustic soda content the pH value of the setting bath should be higher than when using a viscose having a high caustic soda content. When spinning yarn from viscose containing 7% cellulose and 4% sodium hydroxide, it is preferred that the setting bath contain 7% to 12% sodium bisulfite, 7%-l0% sodium sulfite and 8%12% sodium sulfate. When spin hing yarn from viscose containing 7% cellulose and 6% sodium hydroxide, it is preferred that the setting bath contain a slightly greater percentage of sodium bisulfite, for example around and a slightly smaller percentage of sodium sulfite, for example around 3%, thereby lowering the pH value of the bath. The setting bath may, of course, contain other ingredients than those set forth above. For example, they may contain small percentages of glucose, other alkali metal salts and the like. The acidity of the setting bath will be automatically maintained constant for long periods of time in view of the strong bufier ing action of the salts in the bath. Substantial quantities of-sodium hydroxide may be carried over into the bath bythe freshly extruded viscose without imparting appreciable changes in the pH value to the bath. The acidity of the bath may be increased by bubbling sulfur dioxide gas through the same, thus converting sodium sulfite to sodium bisulfite. The bath may be bucked up during the spinning operation by thi procedure. The setting bath may have any desired temperature if the spinning speeds, spinneret hole spacings, viscose composition, bath travel, etc., are adjusted accordingly. Preferably, however, the setting bath is maintained at a substantially constant temperature within the range of 40 0., and C.

The setting bath above-described will have a fast coagulating action with no regenerating action or a slow, delayed regenerating action on the viscose. The yarn is passed through this bath for a distance sufliciently great to insure its substantially complete coagulation without permitting it tobecome appreciably regenerated. The exact length of bath travel to accomplish this is, of course, dependent upon such factors as the viscose composition, bath composition, speed of extrusion and draw-oil, and bath temperature. Bath travels of the order of 50 inches are generally satisfactory.

As above indicated, the yarns must be spun with a high ratio of jet velocity to draw-0d speed. In order that satisfactorily crimped filaments will be formed the jet velocityrdraw-ofl speed ratio should be at least four. This ratio of Jet velocity to draw-off speed may, however, be much higher than four, for example, it may be 8, 10, 12, 20 or even higher, depending upon the efi'ects desired in the finished yarn and/or the properties of the viscose and/or setting bath employed.

The setting baths of the present invention are quite corrosive in nature. It is, therefore, preferred that structural materials which have contact with the bath liquidbe composed of, or lined with, non-corrosive materials, for example, rubber, synthetic rubber, stoneware, glass or the like. Lead lined equipment may be used, but in this case a wetting agent should be added to the setting bath to prevent rapid fouling of spinnerets or to prevent discontinuation of the crimp formation during the spinning operation. Wetting agents of the cation-active type such as cetyl betaine, lauryl trimethyl ammonium" bromide, stearyl trimethyl ammonium bromide are preferred.- The phenomenon of loss in continuity of crimp formation when lead equipment is used, is similar to that described in U. S. Patent No. 2,297,746, and any of the wetting agents mentioned in that patent can be used to advantage in the process of the present invention.

Immediately after leaving the initial setting bath, the coagulated, substantially non-regenerated yarn, which now possesses a permanent three-dimensional crimp, is stretched to at least 150% and preferably'to at least 200% of its original length. This stretching of the yarn can be carried out in any known manner, for example, in the manner disclosed in the illustrations, above-described. The stretching may be carried out in any desired medium, for example, in the air, in an aqueous salt solution, organic liquid or the like. Preferably the stretching is carried out in the presence of a bath of approximately the same composition as the setting bath but maintained at a temperature of between C. and the boiling point thereof.

The stretched yarn is then collected and converted to regenerated cellulose, this conversion preferably being carried out while the yarn is in a relaxed free-to-shrink condition. The regeneration'of the yarn, or the completion of the regeneration thereof, can be carried out in any desired manner including treatment of the yarn in an acid liquid, a boiling salt solution, by heat or the like. The regeneration is preferably carried out by immersing the yarns, in aloose condition, for example in skein form, in a bath similar to the setting bath composition or the stretching bath composition but maintained at a temperature between 80 C., and the boiling point thereof. The yarns are permitted to remain in the regenerating bath until they are auams 7 completely converted to regenerated -cellulose. generally a period of from 10 to 60 minutes.

Following regeneration, the yarn is purified in the usual manner and dried. The drying step, and preferably also the purification step, is carried out with the yarn substantially free of all tension so that the yarn may be free to shrink and develop the maximum amount of crimp. when the yarn is regenerated by treatment with a hot bath of the same composition as the setting bath, the yarn may not require a separate desulfurizing treatment or at least no extensive desulfurizing treatment. since the setting baths of this invention have a considerable desulfurizing effect on the yarn.

In practicing the present invention, it is preferred that the yarn, Just prior to drying. be subjected to treatment with lubricating finish, for example, a textile soap, oil, sulfonated oil, mineral oil or other similar textile finish. The finish appears to favorably affect the crimping of the yarn during drying.

The filaments, fibers and yarns produced in accordance with the present invention not only have a very desirable permanent, three dimensional crimp but have many other outstanding physical characteristics. These fibers and yarns. in comparison to yarns produced by the process of Patent No. 2,249,745, possess relatively high tenacities (between 1.25 and 1.49 grams per denier dry, and 0.50 to 0.71 gram per denier wet), relatively low elongations (between 4% and wet and dry), a spontaneous elongation in water not to exceed 35%, and a secondary swelling in water not to exceed 95%. Yarns produced in accordance with the process of U. S. Patent No. 2,249,745, have a dry tenacity of 0.9 to 1.25 grams per denier, a wet tenacity of 0.4 to 0.6 gram per denier, elongations of 35% to 60% wet and dry, a spontaneous elongation in water of 50%, and a secondary swelling in water of 150%.

The spontaneous elongation in water isdetermined by measuring the length of a sample of the fiber, followed by immersing it in water at room temperature for sufiicient time to permit it to come to equilibrium with the water, and then determining the increase in length of the fiber. (The fiber lengths being measured with the crimp pulled out.) The per cent spontaneous elongation is based on the original length of the dry fiber with the crimp pulled out. The secondary swelling of the fiber is determined by first weighing a sample of the fiber. This is then soaked in room temperature water until equilibrium has been reached. The wet fiber is then centrifuged along with a similarly wet-out fiber with which it is compared in a centrifuge basket having a diameter of 12 inches and a speed of approximately 1500 R. P. M. for 2 minutes. The centrifuged fiber is then reweighed immediately and the percent secondary swelling based on the original dry weight of the sample.

The fibers and filaments produced in accordance with this invention have a permanent crimp by the definition given above with reference to the filaments produced in accordance with the process of U. S. Patent No. 2,249,745. Whether or not a crimp in a filament or fiber is permanent may also be readiLv determined by submersing the filamentous structure in liquid ammonia and permitting it to dry without tension. If the crimp is retained in the structure it must be considered permanent.

The exact reasons for the development of these desirable properties in the yarns of this invention are not clearly understood, although they are believed to be directly related to the particular spinning bath employed which permits greater or more permanent drawing of the gel fibers after coagulation. These baths are similar -to those previously proposed for use in the spinning of permanently crimped regenerated cellulose yarn in that they also exert a rapid coagulating, slow regenerating eflect on the extruded viscose solution. Nevertheless, at the same time they differ from those baths in that they possess a bufi'ering action because of the presence therein of sodium bisulfite. This buffering action, as is well understood, permits the bath to possess a relatively constant pH over extensive periods of use, despite the introduction of large amounts of caustic from the extruded solution, and this action together with an evidently specific eifect of bisulfite on the extruded viscose solution, apparently accounts for the new and desirable properties of the final yarn.

This invention makes possible the spinning of an inherent, permanently crimped regenerated cellulose yarn that possesses a satisfactory tenacity and a desirable elongation, the yarn exhibiting a markedly lower spontaneous elongation in water and secondary swelling than those permanently crimped regenerated cellulose yarns previously produced by the art. The

. yarns of the invention possess a very desirable afiinity for cellulosic dyes.

Because of these desirable properties which are here combined in a single yarn, and particularly because of their low elongation, spontaneous elongation in water and secondary swelling (which properties are considered highly significant and new) the permanently crimped yarns of this invention are especially satisfactory for use in the manufacture of flat fabrics such as suitings, overcoatings, shirtings, etc. Such fabrics do not lose their shape and become uncomfortably wet on exposure to water as do fabrics prepared from previously pr posed permanently crimped cellulose yarns.

The process of the invention is simple of operation and economical. It does not require the use of specialized apparatus. The baths of the invention are not expensive to prepare and maintain, and the sulfite-type bath is especially economical since its preparation involva the use only of sodium hydroxide and sodium suifate. It is readily maintained by passing gaseous SO: into the waste bath. At the same time. because the coagulated, substantially non-regenerated yarns of this invention can be stretched to higher degrees than the corresponding yarns of the prior art, the invention makes possible the production of fine denier crimped filaments. This reduction in filament deniers opens up an entirely new field of use for a permanently crimped regenerated cellulose yarn.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited to those details except as set forth in the appended claims.

I claim:

1. A process for the production of crlmpy filament which comprises extruding viscose, in the form of filaments, into a setting bath having a pH value 01' between 5 and 6.5 and containing between 6% and 20% sodium bisulfite, between 3% and 10% of sodium sulfite and between 8% and 12% of sodium sulfate, drawing the filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of draw-off, stretching said filaments to at least 150% of their originally formed length, and thereafter regenerating said filaments and drying the same while permitting them complete freedom to shrink.

2. A process for the production of crlmpy filaments which comprises extruding viscose, in the form of filaments, into a setting bath having a pH value of between '5 and 6.5 and containing between 6% and 20% sodium bisulfite, between 3% and of sodium sulfite and between 8% and 12% of sodium sulfate, drawing the filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of draw-off, stretching said filaments in a liquid medium to at least 150% of their originally formed length, and thereafter regenerating said filaments and drying the same while permitting them complete freedom to shrink.

3. A process for the production of crlmpy filaments which comprises extruding viscose, in the form of filaments, into a setting bath having a pH value of between 5 and 6.5 and containing between 6% and sodium bisulflte, between 3% and 10% of sodium sulfite and between 8% and 12% of sodium sulfate, drawing the filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of draw-off, stretching said filaments to at least 150% of their originally formed length in a bath having a temperature 10 between 80 C. and the boiling point thereof, said bath containing sodium bisulfite, sodium sulfite and sodium sulfate and having a pH value of between 5 and 6.5, and thereafter regenerating said filament and drying the same while permitting them complete freedom to shrink.

4. A process for the production of crlmpy filaments which comprises extruding viscose, in the form of filaments, into a setting bath having a pH 'value of between 5 and 6.5 and containing between 6% and 20% sodium bisulfite, between 3% and 10% of sodium sulfite and between 8% and 12% of sodium sulfate, drawing the filaments from the point where they are extruded into the bath, the velocity of extrusion being at least four times the velocity of draw-off, stretching said filaments to at least 150% of their originally formed length in a bath having a temperature between 80 C. and the boiling point thereof, said stretching bath being of approximately the same composition as said setting bath, thereafter regenerating said filaments in a bath of similar composition to said stretching bath, and drying the filaments while permitting them complete freedom to shrink.

5. A process for the production of crimpy filaments as defined in claim 1 in which the setting bath has a temperature of between 40 C. and C.

6. A process for the production of crlmpy filaments as defined in'claim 4 in which the bath for regeneration of the filaments has a temperature between C. and the boiling point of the bath composition.

WILLIAM FREDERICK UNDERWOOD. 

